Multichroic glasses with praseodymium and neodymium

ABSTRACT

A glass that includes Pr2O3 and Nd2O3 such that the sum of Pr2O3 and Nd2O3 is greater than 0.2 mole % and the ratio of Nd2O3 to Pr2O3 is greater than 0.5 and less than 3. Further, the sum of any chromophores in the glass from the group V2O5, Cr2O3, MnO, Mn2O3, Fe2O3, CoO, Co3O4, CuO, NiO, Nb2O5, CeO2, Ho2O3 and Er2O3 is less than 0.1 mole %. The glass can be characterized by a substantially pink color upon exposure to an incandescent light source and a substantially green color upon exposure to a fluorescent light source. The glass can optionally include one or more fluorescent ions selected from oxides of Cu, Sn, Mn, Ag, Sb, Ce, Sm, Eu, Tb, Dy, Tm, and combinations thereof, such that a total concentration of fluorescent ions is from greater than or equal to about 0.01 mole % to less than or equal to about 5.0 mole %.

This application claims the benefit of priority under 35 U.S.C. § 365 ofInternational Patent Application Serial No. PCT/US2017/27314, filed onApr. 13, 2017, which claims benefit to U.S. Provisional Application Ser.No. 62/322,562 filed on Apr. 14, 2016, the content of which is reliedupon and incorporated herein by reference in its entirety.

FIELD

The present specification generally relates to color-changing glassesand glass articles comprising color-changing materials and, morespecifically, to customizable, multichroic glasses and glass articlescomprising multichroic materials.

BACKGROUND

Some glass compositions that change color when exposed to varying lightconditions are known. However, the color shift in these glasses is notcustomizable and, thus, they are not suitable for many uses,particularly anti-counterfeiting schemes. Further, the color shift insome of these glasses is not aesthetically pleasing for purposes of artand or decorative applications.

Various anti-counterfeiting schemes have been developed for consumerproducts including fine wine, watches, jewelry and other productssubject to high volumes of counterfeiting activities. Many of theseschemes rely on “black box” sensors to determine if a particular good isgenuine or counterfeit. Unfortunately, these schemes suffer from theprevalence of counterfeit “black boxes” that provide false indicationsthat a particular good is genuine.

Therefore, glasses with controlled, color-changing capabilities whenexposed to varying light conditions have a number of desirableapplications. Further, anti-counterfeiting schemes that can be useddirectly by a consumer without the need for additional sensors are alsodesirable.

SUMMARY

According to one embodiment, a glass is provided that includes Pr₂O₃ andNd₂O₃ such that the sum of Pr₂O₃ and Nd₂O₃ is greater than 0.2 mole %and the ratio of Nd₂O₃ to Pr₂O₃ is greater than 1 and less than 1.9.Further, CoO, if present, is less than 0.01 mole % and Fe₂O₃, ifpresent, is less than 0.004 mole %. The glass can optionally include oneor more fluorescent ions selected from the group consisting of oxides ofYb, Cu, Sn, Mn, Ag, Sb, Ce, Sm, Eu, Tb, Dy, Tm, and combinationsthereof, such that a total concentration of fluorescent ions is fromgreater than or equal to about 0.01 mole % to less than or equal toabout 5.0 mole %. Further, the glass can optionally include at least onechromophore selected from the group consisting of V₂O₅, Cr₂O₃, MnO,Mn₂O₃, Fe₂O₃, CoO, Co₃O₄, CuO, NiO, Nb₂O₅, CeO₂, Ho₂O₃ and Er₂O₃, suchthat the sum of V₂O₅, Cr₂O₃, MnO, Mn₂O₃, Fe₂O₃, CoO, Co₃O₄, CuO, NiO,Nb₂O₅, CeO₂, Ho₂O₃ and Er₂O₃ is less than 0.1 mole %.

In another embodiment, a glass is provided that includes Pr₂O₃ and Nd₂O₃such that the sum of Pr₂O₃ and Nd₂O₃ is greater than 0.2 mole % and theratio of Nd₂O₃ to Pr₂O₃ is greater than 0.5 and less than 3. Further,the sum of V₂O₅, Cr₂O₃, Mn₂O₃, Fe₂O₃, CoO, Co₃O₄, CuO, NiO, Nb₂O₅, CeO₂,Ho₂O₃ and Er₂O₃ chromophores in the glass, if any of these chromophoresare present, is less than 0.1 mole %. The glass can optionally includeone or more fluorescent ions selected from the group consisting ofoxides of Yb, Cu, Sn, Mn, Ag, Sb, Ce, Sm, Eu, Tb, Dy, Tm, andcombinations thereof, such that a total concentration of fluorescentions is from greater than or equal to about 0.01 mole % to less than orequal to about 5.0 mole %. Further, an aspect of this glass includes atleast one chromophore selected from the group consisting of V₂O₅, Cr₂O₃,MnO, Mn₂O₃, Fe₂O₃, CoO, Co₃O₄, CuO, NiO, Nb₂O₅, CeO₂, Ho₂O₃ and Er₂O₃.

In a further embodiment, a glass is provided that includes Pr₂O₃ andNd₂O₃ such that the sum of Pr₂O₃ and Nd₂O₃ is greater than 0.2 mole %and the ratio of Nd₂O₃ to Pr₂O₃ is greater than or equal to 0.9 and lessthan or equal to 2.0. Further, Ce₂O₃, if present, is less than 1 mole %,Fe₂O₃, if present, is less than 0.4 mole %, Mn₂O₃, if present, is lessthan 0.04 mole %, Er₂O₃, if present, is less than 1 mole %, and Nb₂O₅,if present, is less than 0.5 mole %. The glass can optionally includeone or more fluorescent ions selected from the group consisting ofoxides of Yb, Cu, Sn, Mn, Ag, Sb, Ce, Sm, Eu, Tb, Dy, Tm, andcombinations thereof, such that a total concentration of fluorescentions is from greater than or equal to about 0.01 mole % to less than orequal to about 5.0 mole %. Further, the glass can optionally include atleast one chromophore selected from the group consisting of V₂O₅, Cr₂O₃,MnO, Mn₂O₃, Fe₂O₃, CoO, Co₃O₄, CuO, NiO, Nb₂O₅, CeO₂, Ho₂O₃ and Er₂O₃,such that the sum of V₂O₅, Cr₂O₃, MnO, Mn₂O₃, Fe₂O₃, CoO, Co₃O₄, CuO,NiO, Nb₂O₅, CeO₂, Ho₂O₃ and Er₂O₃ is less than 0.1 mole %.

In an additional embodiment, a glass is provided that includes SiO₂ atgreater than 70 mole %, along with Pr₂O₃ and Nd₂O₃ such that the sum ofPr₂O₃ and Nd₂O₃ is greater than 0.2 mole % and the ratio of Nd₂O₃ toPr₂O₃ is greater than 0.5 and less than 3. Further, the sum of Fe₂O₃,CeO₂, and TiO₂, if any are present, is less than 1 mole %. The glass canoptionally include one or more fluorescent ions selected from the groupconsisting of oxides of Yb, Cu, Sn, Mn, Ag, Sb, Ce, Sm, Eu, Tb, Dy, Tm,and combinations thereof, such that a total concentration of fluorescentions is from greater than or equal to about 0.01 mole % to less than orequal to about 5.0 mole %. Further, the glass can optionally include atleast one chromophore selected from the group consisting of V₂O₅, Cr₂O₃,MnO, Mn₂O₃, Fe₂O₃, CoO, Co₃O₄, CuO, NiO, Nb₂O₅, CeO₂, Ho₂O₃ and Er₂O₃,such that the sum of V₂O₅, Cr₂O₃, MnO, Mn₂O₃, Fe₂O₃, CoO, Co₃O₄, CuO,NiO, Nb₂O₅, CeO₂, Ho₂O₃ and Er₂O₃ is less than 0.1 mole %.

In further embodiments, any of the foregoing glasses can becharacterized by a first color upon exposure to an incandescent lightsource and a second color upon exposure to a fluorescent light source,the first and second colors distinct from one another. For example, thefirst color is substantially pink and the second color is substantiallygreen in an aspect of these glasses. In addition, aspects of theseglasses can be further characterized by a color difference (CD) of atleast 3.0 from being subjected to a D65-10 illumination condition and anF02-10 illumination condition.

In another aspect of these glasses, the ratio of Nd₂O₃ to Pr₂O₃ isgreater than 0.75 and less than 2.0. In another aspect, the ratio ofNd₂O₃ to Pr₂O₃ is greater than 1.1 and less than 1.9. Further, inadditional aspects, the Pr₂O₃ can range from about 0.7 to about 3.0 mole% and the Nd₂O₃ can range from about 1.0 to about 4 mole % in certainimplementations.

In a further aspect of the disclosure, a glass article is provided thatincludes a first multichroic portion having a first glass composition;and a second multichroic portion having a second glass compositioncomprising a composition that differs from the first glass composition.The first glass composition includes Pr₂O₃ and Nd₂O₃ such that the sumof Pr₂O₃ and Nd₂O₃ is greater than 0.2 mole % and the ratio of Nd₂O₃ toPr₂O₃ is greater than 0.5 and less than 3. Further, the sum of V₂O₅,Cr₂O₃, Mn₂O₃, Fe₂O₃, CoO, Co₃O₄, CuO, NiO, Nb₂O₅, CeO₂, Ho₂O₃ and Er₂O₃chromophores in the glass, if any of these chromophores are present, isless than 0.1 mole %. In certain aspects, the first and secondmultichroic portions cause a pattern in the article to appear ordisappear upon being subjected to an illuminant change from a firstilluminant to a second illuminant.

In an additional aspect of the disclosure, a glass article is providedthat includes a substrate comprising a glass according to any of theforegoing compositions. The substrate further comprises a compressivestress region having a maximum compressive stress of at least 50 MPa anda depth of layer (DOL) of at least 15 microns in thickness.

In another aspect of the disclosure, a glass article is provided thatincludes a container comprising a glass according to any of theforegoing compositions. Further, the container is configured to containat least one liquid or solid medium. In some aspects, the container isconfigured as a perfume bottle, a cologne bottle, a medicine bottle, oran electronic device case. In an additional aspect, the glass is furtherconfigured for an anti-counterfeiting system.

Additional features and advantages will be set forth in the detaileddescription which follows, and in part will be readily apparent to thoseskilled in the art from that description or recognized by practicing theembodiments described herein, including the detailed description whichfollows, the claims, as well as the appended drawings.

It is to be understood that both the foregoing general description andthe following detailed description describe various embodiments and areintended to provide an overview or framework for understanding thenature and character of the claimed subject matter. The accompanyingdrawings are included to provide a further understanding of the variousembodiments, and are incorporated into and constitute a part of thisspecification. The drawings illustrate the various embodiments describedherein, and together with the description serve to explain theprinciples and operations of the claimed subject matter.

DETAILED DESCRIPTION

It is therefore desirable to provide glasses with controlled,color-changing capabilities when subjected to, exposed to, or otherwiseilluminated by varying light conditions. It is also desirable to provideinexpensive anti-counterfeit schemes that can be incorporated into anarticle that allow a purchaser to more easily determine whether a goodis genuine or counterfeit.

Accordingly, color-changing glasses of the disclosure offer one or moreof the following advantages. For example, color-changing glassembodiments do not require expensive gemstones or single crystaladditives to achieve color shifts. Further, the varying light conditionsthat impart color changes in glasses of the disclosure are readilyavailable to the consumer. These conditions include full spectrum light(e.g., sunlight and incandescent light) and the narrow atomic emissionlines of fluorescent lighting. RGB white light from LEDs and mobiledevice displays provide yet another illumination source that can impartan additional color. The anti-counterfeiting schemes offered by glassesof the disclosure can rely on the human eye, without the need foradditional sensors that themselves could be counterfeit. Another benefitof glasses of the disclosure is that their color-shifts are interestingand can be tailored for particular decorative or artistic effects. Afurther benefit is that artistic articles can contain multiple glasscompositions of the disclosure to produce interesting patterns (e.g., inlayered composites). These patterns can either switch color with theirbackground, or disappear or appear as the illumination conditions arechanged. Another benefit is that the base glass composition is flexible,which can include ion exchangeable and damage resistant compositions(e.g., Corning Inc.® Gorilla Glass®) and inexpensive soda lime silicatecompositions.

Reference will now be made in detail to embodiments that include acolor-changing glass comprising Pr₂O₃ and Nd₂O₃ such that the sum ofPr₂O₃ and Nd₂O₃ is greater than 0.2 mole % and the ratio of Nd₂O₃ toPr₂O₃ is greater than 0.5 and less than 3. Each of Pr₂O₃ and Nd₂O₃ maybe set from about 0.065% to about 20 mole %. The glass can include oneor more visibly fluorescent ions selected from oxides of Yb, Cu, Sn, Mn,Ag, Sb, Ce, Sm, Eu, Tb, Dy, Tm, and combinations thereof, such that atotal concentration of fluorescent ions is from greater than or equal toabout 0.01 mole % to less than or equal to about 5.0 mole %. Thefluorescence can be in the visible spectrum (e.g., Tb³⁺ emits orotherwise fluoresces green light), thus facilitating consumerauthentication, for example, in an anti-counterfeiting scheme, securityapparatus or the like. The fluorescence can also be in the infraredspectrum (e.g., Yb³⁺ emits or otherwise fluoresces light at 976 nm and1060 nm), thus facilitating authentication, for example, by a consumer(e.g., to the extent possessing such infrared light-emitting equipment)or other authorized individual in an anti-counterfeiting scheme,security apparatus or the like, for example. Further, the glass caninclude no chromophores or at least one chromophore selected from V₂O₅,Cr₂O₃, MnO, Mn₂O₃, Fe₂O₃, CoO, Co₃O₄, NiO, CuO, Nb₂O₅, CeO₂, Ho₂O₃ andEr₂O₃, such that the sum of the chromophore(s) is less than 0.1 mole %.Various embodiments of color changing glasses will be described in moredetail herein.

According to one embodiment, a color-changing glass is provided thatincludes Pr₂O₃ and Nd₂O₃ such that the sum of Pr₂O₃ and Nd₂O₃ is greaterthan 0.2 mole % and the ratio of Nd₂O₃ to Pr₂O₃ is greater than 1 andless than 1.9. Further, CoO, if present, is less than 0.01 mole % andFe₂O₃, if present, is less than 0.004 mole %. The glass can optionallyinclude one or more fluorescent ions selected from the group consistingof oxides of Yb, Cu, Sn, Mn, Ag, Sb, Ce, Sm, Eu, Tb, Dy, Tm, andcombinations thereof, such that a total concentration of fluorescentions is from greater than or equal to about 0.01 mole % to less than orequal to about 5.0 mole %. Further, the glass can optionally include atleast one chromophore selected from the group consisting of V₂O₅, Cr₂O₃,MnO, Mn₂O₃, Fe₂O₃, CoO, Co₃O₄, CuO, NiO, CuO, Nb₂O₅, CeO₂, Ho₂O₃ andEr₂O₃, such that the sum of V₂O₅, Cr₂O₃, MnO, Mn₂O₃, Fe₂O₃, CoO, Co₃O₄,CuO, NiO, Nb₂O₅, CeO₂, Ho₂O₃ and Er₂O₃ is less than 0.1 mole %.

In another embodiment, a color-changing glass is provided that includesPr₂O₃ and Nd₂O₃ such that the sum of Pr₂O₃ and Nd₂O₃ is greater than 0.2mole % and the ratio of Nd₂O₃ to Pr₂O₃ is greater than 0.5 and less than3. Further, the sum of V₂O₅, Cr₂O₃, MnO, Mn₂O₃, Fe₂O₃, CoO, Co₃O₄, CuO,NiO, Nb₂O₅, CeO₂, Ho₂O₃ and Er₂O₃ chromophores in the glass, if any ofthese chromophores are present, is less than 0.1 mole %. The glass canoptionally include one or more fluorescent ions selected from the groupconsisting of oxides of Yb, Cu, Sn, Mn, Ag, Sb, Ce, Sm, Eu, Tb, Dy, Tm,and combinations thereof, such that a total concentration of fluorescentions is from greater than or equal to about 0.01 mole % to less than orequal to about 5.0 mole %. Further, an aspect of this glass includes atleast one chromophore selected from the group consisting of V₂O₅, Cr₂O₃,MnO, Mn₂O₃, Fe₂O₃, CoO, Co₃O₄, CuO, NiO, Nb₂O₅, CeO₂, Ho₂O₃ and Er₂O₃.

In a further embodiment, a color-changing glass is provided thatincludes Pr₂O₃ and Nd₂O₃ such that the sum of Pr₂O₃ and Nd₂O₃ is greaterthan 0.2 mole % and the ratio of Nd₂O₃ to Pr₂O₃ is greater than or equalto 0.9 and less than or equal to 2.0. Further, Ce₂O₃, if present, isless than 1 mole %, Fe₂O₃, if present, is less than 0.4 mole %, Mn₂O₃,if present, is less than 0.04 mole %, Er₂O₃, if present, is less than 1mole %, and Nb₂O₅, if present, is less than 0.5 mole %. The glass canoptionally include one or more fluorescent ions selected from the groupconsisting of oxides of Yb, Cu, Sn, Mn, Ag, Sb, Ce, Sm, Eu, Tb, Dy, Tm,and combinations thereof, such that a total concentration of fluorescentions is from greater than or equal to about 0.01 mole % to less than orequal to about 5.0 mole %. Further, the glass can optionally include atleast one chromophore selected from the group consisting of V₂O₅, Cr₂O₃,MnO, Mn₂O₃, Fe₂O₃, CoO, Co₃O₄, CuO, NiO, Nb₂O₅, CeO₂, Ho₂O₃ and Er₂O₃,such that the sum of V₂O₅, Cr₂O₃, MnO, Mn₂O₃, Fe₂O₃, CoO, Co₃O₄, CuO,NiO, Nb₂O₅, CeO₂, Ho₂O₃ and Er₂O₃ is less than 0.1 mole %.

In an additional embodiment, a color-changing glass is provided thatincludes SiO₂ at greater than 70 mole %, along with Pr₂O₃ and Nd₂O₃ suchthat the sum of Pr₂O₃ and Nd₂O₃ is greater than 0.2 mole % and the ratioof Nd₂O₃ to Pr₂O₃ is greater than 0.5 and less than 3. Further, the sumof Fe₂O₃, CeO₂, and TiO₂, if any are present, is less than 1 mole %. Tothe extent that Mn₂O₃ and NiO are present in the glass, the sum ofMn₂O₃, Fe₂O₃, NiO and CeO₂ should be less than 2 mole %. The glass canoptionally include one or more fluorescent ions selected from the groupconsisting of oxides of Yb, Cu, Sn, Mn, Ag, Sb, Ce, Sm, Eu, Tb, Dy, Tm,and combinations thereof, such that a total concentration of fluorescentions is from greater than or equal to about 0.01 mole % to less than orequal to about 5.0 mole %. Further, the glass can optionally include atleast one chromophore selected from the group consisting of V₂O₅, Cr₂O₃,MnO, Mn₂O₃, Fe₂O₃, CoO, Co₃O₄, NiO, CuO, Nb₂O₅, CeO₂, Ho₂O₃ and Er₂O₃,such that the sum of V₂O₅, Cr₂O₃, MnO, Mn₂O₃, Fe₂O₃, CoO, Co₃O₄, NiO,CuO, Nb₂O₅, CeO₂, Ho₂O₃ and Er₂O₃ is less than 0.1 mole %.

Embodiments of the glasses disclosed herein are directed tocolor-changing glasses, such as, for example, color-changingaluminosilicate glasses and color-changing alkali aluminosilicateglasses. The composition of the silicate glasses, according toembodiments, is outlined below; however, it should be understood thatthe composition of the glasses is not particularly limited to silicateglasses and that the chromophores and fluorescent compounds can be addedto other types of glass-ceramics, polymers, single crystals, andglasses, including, without limitation, borate glasses, phosphateglasses, fluoride glasses, tellurate glasses, and aluminate glasses. Insome embodiments, chalcogenide glasses, such as, for example, sulfideglasses, can be used. In other embodiments, any materials that are notstrongly absorbing in the visible light spectrum can be used.

As used herein, “multichroic” relates to a capability of a glass toexhibit a shift in color upon illumination with different light sourcesthat include a spectral change and/or an intensity change. As usedherein, “metamerism” relates to a capability of a glass to exhibit ashift in color upon being subjected to, exposed to or otherwiseilluminated with, a first and a second, illuminant. As used herein, the“Color Difference (CD)” or “color difference (CD)” shows the colordifference between two different illuminants. The color difference (CD)is given by Equation (1):CD=√{square root over ((L* ₁ −L* ₂)²+(a* ₁ −a* ₂)²+(b* ₁ −b* ₂)²)}  (1)where L*₁, a*₁, b*₁ are the CIELab* color coordinates (i.e., as adoptedby the International Commission on Illumination in 1976) under the firstilluminant (e.g., a D65 illuminant) and L*₂, a*₂, b*₂ are the CIELab*color coordinates on the same sample under the second illuminant (e.g.,an F02 illuminant). Further, all color difference (CD) measurementsreported herein were obtained by measuring samples cut into 40×40 mmsquares with a thickness of 2 mm and polished on both sides with ceriumoxide polishing media. Color coordinates were then measured with aparticular illuminant (e.g., F02 illuminant) in a reflectance modethrough the thickness of each sample on an X-Rite Color i7™ BenchtopSpectrophotometer with a white backing substrate situated behind eachsample.Praseodymium- and Neodymium-Containing Glasses

In an exemplary silicate glass composition, SiO₂ is the largestconstituent and, as such, SiO₂ is the primary constituent of the glassnetwork formed from the glass composition. Pure SiO₂ has a relativelylow coefficient of thermal expansion (CTE). However, pure SiO₂ has ahigh melting point. Accordingly, if the concentration of SiO₂ in theglass composition is too high, the formability of the glass compositioncan be diminished as higher concentrations of SiO₂ increase thedifficulty of melting the glass, which, in turn, adversely impacts theformability of the glass. Low SiO₂ glasses, such as, for example, glasswith less than 40 mole % SiO₂, tend to have poor durability andresistance to devitrification, so it is practical to have more than 40%SiO₂ and more than 50% SiO₂ for ease of forming. Glasses with at least70 mole % SiO₂ have excellent durability and are suitable for exteriorapplications and installations. However, it should be understood thatglasses that do not include silica can also be used in embodiments. Forexample, phosphate glasses, borate glasses, heavy metal fluoride, andother non-silica glasses could be used according to embodiments.

In embodiments, the glass composition can comprise SiO₂ in aconcentration from greater than or equal to about 40 mole % to less thanor equal to about 80 mole %, for example, from greater than or equal toabout 50 mole % to less than or equal to about 75 mole %. In otherembodiments, the glass composition can comprise SiO₂ in a concentrationfrom greater than or equal to about 55 mole % to less than or equal toabout 70 mole %, such as from greater than or equal to about 62 mole %to less than or equal to about 69 mole %. In further embodiments, theglass composition can comprise SiO₂ in a concentration from greater thanor equal to 70 mole % (e.g., for added durability).

As discussed above, embodiments of the glass composition are directed toaluminosilicate glasses. Thus, the glass composition of embodiments canfurther comprise Al₂O₃ in addition to SiO₂. Al₂O₃ can serve as a glassnetwork former, similar to SiO₂. Al₂O₃ can increase the viscosity of theglass composition due to its tetrahedral coordination in a glass meltformed from a properly designed glass composition. However, when theconcentration of Al₂O₃ is balanced against the concentration of SiO₂and, optionally, the concentration of alkali oxides in the glasscomposition, Al₂O₃ can reduce the liquidus temperature of the glassmelt, thereby enhancing the liquidus viscosity and improving thecompatibility of the glass composition with certain forming processes.The Al₂O₃ also serves as an aid to increase the solubility of rare earthdopants, particularly the Pr and Nd in the glass, along with otheroptional rare earth dopants such as Ho, Ce, Sm, Eu, Tb, Dy, and Tm.Thus, for glasses where shorter optical path lengths or thinner articlesare desired, more of the combination of Pr₂O₃ and Nd₂O₃ is needed, soglasses with more than 1 mole % Al₂O₃ are desirable. For glasses withmore than 10 mole % (Pr₂O₃+Nd₂O₃) it is desirable to have at least 10mole % Al₂O₃. When the Al₂O₃ concentration exceeds 30 mole %, theliquidus temperature of the glass increases and the formability of theglass suffers. As such, it is generally desirable to employ less than 30mole % Al₂O₃ for ease of forming the glass and less than 20 mole % Al₂O₃for fabricating larger volumes of the glasses of the disclosure (e.g.,in a manufacturing-scale operation). In pure SiO₂, rare earth oxidecontents greater than 500-1000 ppm can result in phase separation ordevitrification, but aluminosilicates can have up to 25 mole % rareearth oxide(s) and still be stable, e.g., as outlined in Hwa, L. G. etal., 39 Material Research Bulletin 33 (2004); and Clayden N. J. et al.,258 J. Non-Crystalline Solids 11 (1999), hereby incorporated byreference in their entirety. In addition, Al₂O₃ can enhance the ionexchange performance of alkali silicates. For chemically strengthenedalkali aluminosilicate glasses, the Al₂O₃ content can be between 5 and25 mole %.

In embodiments, the glass composition can comprise Al₂O₃ in aconcentration from greater than or equal to about 5.0 mole % to lessthan or equal to about 25 mole %, such as from greater than or equal toabout 7.0 mole % to less than or equal to about 17 mole %. In otherembodiments, the glass composition can comprise Al₂O₃ in a concentrationfrom greater than or equal to about 8.0 mole % to less than or equal toabout 14 mole %, such as from greater than or equal to about 9.0 mole %to less than or equal to about 10 mole %. However, it should beunderstood that the glass system is not particularly limited and, thus,in some embodiments, glasses that contain from greater than or equal toabout 25% to less than or equal to about 50% Al₂O₃ can be used. In otherembodiments, the glass system can include no Al₂O₃.

Na₂O is a component that can lower the viscosity of a glass to improvethe meltability and the formability thereof. When the content of Na₂O istoo large, the coefficient of thermal expansion (CTE) of the glassbecomes too large, and the thermal shock resistance of the glass can belowered. Alkali oxides like Li₂O, Na₂O, K₂O, Rb₂O, and Cs₂O can alsoenable ion exchange for modifying both the stress and refractive indexprofiles of the glass, which can enable chemical strengthening andwriting of waveguides via ion exchange that can provide additionalsecurity features. For example, alkali-containing glasses can be ionexchanged in a bath containing Ag⁺ ions such that the Ag⁺ ions willexchange with the monovalent alkalis in the glass thereby incorporatingAg⁺ ions into the glass. The Ag⁺ ions incorporated into the glass willraise the refractive index of glasses containing one or more of Li₂O,Na₂O, K₂O and Rb₂O and also emit or otherwise fluoresce a green colorwhen exposed to ultraviolet (UV) excitation light. The ion exchange canbe patterned by masking portion(s) of the glass exposed to the bathcontaining Ag⁺ ions to create patterns of Ag⁺ waveguides orfluorescence. Alkali oxides do not add color to the glass and have anegligible effect on metamerism or fluorescence. In the case of glasseswhich serve as substrates for Si-based electronics, such as LCDdisplays, alkali ions, such as Na⁺, can poison the Si transistors anddegrade performance; consequently, for these applications, it can bedesirable to have alkali-free compositions.

In embodiments, the glass composition can comprise Na₂O in aconcentration from greater than or equal to about 5 mole % to less thanor equal to about 25 mole %, such as from greater than or equal to about10 mole % to less than or equal to about 20 mole %. In otherembodiments, the glass composition can comprise Na₂O in a concentrationfrom greater than or equal to about 11 mole % to less than or equal toabout 17 mole %, such as from greater than or equal to about 12 mole %to less than or equal to about 15 mole %. In yet other embodiments, theglass composition can comprise Na₂O in a concentration of about 14 mole%.

The glass composition can, in some embodiments, contain other elements,such as alkaline earth metal oxides. In embodiments, the alkaline earthmetal oxides can be selected from MgO, CaO, SrO, BaO, and combinationsthereof. These oxides can be added to increase meltability, durability,and glass stability. While ZnO is not an alkaline earth, it is adivalent oxide and serves a similar function as the above alkaline earthmetal oxides and, thus, ZnO can be added to the glass composition. Thealkaline earth metal oxides can be added as stabilizers that helpprevent degradation of the glass composition upon exposure toenvironmental conditions. However, adding too much alkaline earth metaloxide to the glass composition can decrease its formability.

In embodiments, the glass composition comprises alkaline earth metaloxides in concentrations from greater than or equal to 0.0 mole % toless than or equal to about 25 mole %, such as from greater than orequal to about 2.0 mole % to less than or equal to about 20 mole %. Inother embodiments, the glass composition comprises alkaline earth metaloxides in concentrations from greater than or equal to about 10 mole %to less than or equal to about 17 mole %, such as from greater than orequal to about 12 mole % to less than or equal to about 15 mole %.

In embodiments, the glass composition can comprise B₂O₃ (also referredherein as “boron oxide”). B₂O₃ softens the glass, can increase thesolubility of rare earth dopants, and makes the glass easier to melt andform. However, at very high concentrations of B₂O₃, the glass durabilitysuffers and can phase separate. Accordingly, it is preferable tomaintain the B₂O₃ content below 25 mole %. B₂O₃ is also useful forlowering the coefficient of thermal expansion (CTE) and the liquidustemperature of the glass. In some embodiments, the glass composition cancomprise B₂O₃ in concentrations from greater than or equal to 0.0 mole %(e.g., as including trace amounts or less) to less than or equal toabout 25 mole %. In an implementation, the glass can include B₂O₃ inconcentrations from greater than or equal to about 1.0 mole % to lessthan or equal to about 20 mole %. In other embodiments, the glasscomposition comprises B₂O₃ in concentrations from greater than or equalto about 1.5 mole % to less than or equal to about 10 mole %. Forexample, such glasses in certain embodiments can include a B₂O₃concentration level from greater than or equal to about 7 mole % to lessthan or equal to about 17 mole %.

In embodiments, the glass composition can comprise fining agents, suchas, for example, SnO₂, sulfates, chlorides, bromides, Sb₂O₃, As₂O₃, andCeO₂. At high concentrations, CeO₂ can impart color and overwhelm themultiple colors that would otherwise be exhibited by a glass intended tohave a multichroic capability. Accordingly, the concentration of CeO₂should be limited to less than 1 mole % for high concentrations of Prand Nd in the glass, e.g., where the sum of Pr₂O₃ and Nd₂O₃ exceeds 5mole %. For more intermediate concentrations of Pr and Nd in the glass,e.g., where the sum of Pr₂O₃ and Nd₂O₃ is between 1 and 5 mole %, theconcentration of CeO₂ should be limited to less than 0.5 mole %. Forlower concentrations of Pr and Nd in the glass, e.g., where the sum ofPr₂O₃ and Nd₂O₃ is less than 1 mole %, the concentration of CeO₂ shouldbe limited to less than 0.1 mole %. Ce ions create the most color andabsorption when there is a mixture of Ce³⁺ and Ce⁴⁺ ions in the glass,and the absorption intensity scales with the product of theirconcentrations; consequently, it is desirable to either strongly oxidizethe glass containing Ce to maintain most, if not all, of the Ce in aCe⁴⁺ state or strongly reduce the glass to maintain most, if not all, ofthe Ce in a Ce³⁺ state to minimize the masking effect of the Ce in theglass. The strongly reducing conditions also increase glue luminescencesince Ce³⁺ has a blue fluorescence while Ce⁴⁺ does not. With regard toSnO₂, chlorides, bromides, Sb₂O₃ and As₂O₃, these fining agents do notimpart much color to the glass, but their solubility limits their use tobelow about 1 mole % or less. However, Sn²⁺ and Sb³⁺ ions both fluorescea bluish white color that can be combined with the multichroic effect ofthe glass of this disclosure (e.g., as pertaining to the Pr andNd-related contributions) for additional anti-counterfeiting features,security features or the like. More generally, fining agents can beemployed in the glasses of the disclosure at levels between about 0.05to about 5 mole % to provide the fining function and, in certaininstances, also provide fluorescence (e.g., for Sn²⁺ and Sb³⁺-containingfining agents). In a preferred aspect, SnO₂ is selected as a finingagent as it is not toxic (e.g., as compared to Sb₂O₃ and As₂O₃). Inembodiments, the glass composition can comprise fining agents inconcentrations from greater than or equal to 0.0 mole % to less than orequal to about 1.0 mole %, such as from greater than or equal to about0.002 mole % to less than or equal to about 0.9 mole %. In otherembodiments, the glass composition can comprise fining agents inconcentrations from greater than or equal to about 0.05 mole % to lessthan or equal to about 0.8 mole %, such as from greater than or equal toabout 0.1 mole % to less than or equal to about 0.7 mole %. In yet otherembodiments, the glass composition can comprise fining agents inconcentrations from greater than or equal to about 0.1 mole % to lessthan or equal to about 0.3 mole %, such as about 0.15 mole %. Inembodiments that use sulfates as the fining agents, the sulfates can beincluded in amounts from greater than or equal to about 0.001 mole % toless than or equal to about 0.1 mole %. It should be noted that, asdiscussed below, embodiments may also include Sn²⁺ as fluorescent ions.Therefore, in embodiments, SnO₂ will not be used as a fining agent sothat it does not interfere with the fluorescent properties of the glass.Additionally, in embodiments where Sn ions are used as fluorescents, theconcentration of Sn ions can be balanced with other fining agents.

In addition to the above silicate glass components, glass compositionsaccording to embodiments described herein further comprise Pr₂O₃ andNd₂O₃. The addition of a combination of Pr₂O₃ and Nd₂O₃ adds color and acolor-changing capability to the glass composition. In these glasses,the sum of Pr₂O₃ and Nd₂O₃ is greater than 0.2 mole % and the ratio ofNd₂O₃ to Pr₂O₃ is greater than 0.5 and less than 3 to achieve acolor-changing capability. Each of Pr₂O₃ and Nd₂O₃ may be set from about0.065% to about 20 mole %. At these levels of Pr₂O₃ and Nd₂O₃, theseglasses exhibit a pink color when observed in daylight, incandescent orfull spectrum white light. When observed under a typical fluorescentlight source (e.g., with sharp emission bands at about 545 nm and 620nm), these glasses exhibit a green color. Further, when illuminated withan LED flashlight or LED lighting fixture (e.g., blue LED with Ce:YAGyellow phosphor), these glasses appear yellow. Hence, these glasses aremultichroic, capable of changing from pink-to-green-to-yellow orchanging in other sequences of pink, green and yellow, depending on theillumination conditions (e.g., spectra of the light source illuminatingthem).

In another preferred aspect, a large color shift can be observed inglasses of the disclosure with the Nd₂O₃/Pr₂O₃ ratio between 0.75 and2.0. Other aspects of the disclosure are directed to glass compositionswith the Nd₂O₃/Pr₂O₃ ratio between 1 and 1.9. Another aspect of thedisclosure is directed to glass composition with the Nd₂O₃/Pr₂O₃ ratioset at greater than or equal to 0.9 and less than or equal to 2.0. Evenmore dramatic color changes are possible in some embodiments of theseglasses in which the Nd₂O₃/Pr₂O₃ ratio is between 1.1 and 1.5.

When the Nd₂O₃/Pr₂O₃ ratio is less than 0.5, the green Pr₂O₃ colordominates and these color changes are weakly observed. Conversely, whenthe Nd₂O₃/Pr₂O₃ ratio is greater than 4, the purple Nd₂O₃ colordominates and the color changes are weakly observed. As such, theNd₂O₃/Pr₂O₃ ratio should be generally controlled within 0.5 to 4 toensure that the glass exhibits a significant multichroic, color-changingcapability. Accordingly, in certain implementations of the glasses ofthe disclosure, the Nd₂O₃/Pr₂O₃ ratio can be set at 0.5, 0.6, 0.7, 0.8,0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, 2.1, 2.2,2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9, 3.0, 3.1, 3.2, 3.3, 3.4, 3.5, 3.6,3.7, 3.8, 3.9, 4.0 and all ratios between these examples.

In certain preferred implementations, the Pr₂O₃ can range from about 0.7to about 3 mole % and the Nd₂O₃ can range from about 1.0 to about 4 mole%, to obtain a color-changing effect. For example, the Pr₂O₃ can be setat 0.5 mole %, 0.6 mole %, 0.7 mole %, 0.8 mole %, 0.9 mole %, 1.0 mole%, 1.1 mole %, 1.2 mole %, 1.3 mole %, 1.4 mole %, 1.5 mole %, 1.6 mole%, 1.7 mole %, 1.8 mole %, 1.9 mole %, 2.0 mole %, 2.1 mole %, 2.2 mole%, 2.3 mole %, 2.4 mole %, 2.5 mole %, 2.6 mole %, 2.7 mole %, 2.8 mole%, 2.9 mole %, 3.0 mole %, and all values between these amounts.Similarly, the Nd₂O₃ can be set at, for example, 1.0 mole %, 1.1 mole %,1.2 mole %, 1.3 mole %, 1.4 mole %, 1.5 mole %, 1.6 mole %, 1.7 mole %,1.8 mole %, 1.9 mole %, 2.0 mole %, 2.1 mole %, 2.2 mole %, 2.3 mole %,2.4 mole %, 2.5 mole %, 2.6 mole %, 2.7 mole %, 2.8 mole %, 2.9 mole %,3.0 mole %, 3.1 mole %, 3.2 mole %, 3.3 mole %, 3.4 mole %, 3.5 mole %,3.6 mole %, 3.7 mole %, 3.8 mole %, 3.9 mole %, 4.0 mole %, and allvalues between these amounts. In an additional preferred aspect, thePr₂O₃ can range from about 0.5 mole % to about 1 mole % and the Nd₂O₃can range from about 1 mole % to about 2 mole % to obtain a strong,color-changing effect. Still further, other aspects of the glasses inthe disclosure can include Pr₂O₃ levels above 3 mole % and Nd₂O₃ levelsabove 4 mole %. These higher levels of Pr₂O₃ above 3 mole % and Nd₂O₃above 4 mole % are particularly suited for thin glasses and glassarticles in which the costs of the Pr and Nd additives can be limited.These higher levels of Pr₂O₃ above 3 mole % and Nd₂O₃ above 4 mole % arealso suited for thin glasses given that the intensity of color is afunction of the dopant level and the thickness of the glass article. Assuch, thinner glass articles require increasingly higher concentrationsof dopants to achieve the same color intensity levels of thicker glassarticles. From a practical standpoint, the total concentration of Pr₂O₃and Nd₂O₃ can be limited to about 50 mole %, (e.g., within thin glassarticles), as higher levels of rare earth oxides in the glass can makethe glass unstable and prone to crystallization.

Pure Nd- & Pr-doped glasses can change in appearance from pink to greenwith a change in illumination from incandescent or daylight (i.e., a D65standard illuminant) to fluorescent light (i.e., an F02 standardilluminant). Certain aspects of these glasses with the Nd₂O₃/Pr₂O₃ ratioat about 1.222 exhibit a color difference (CD) of 8.8 with a change inillumination from incandescent or daylight to fluorescent light (see,e.g., Ex. 1 in Tables 1 and 2). Thus, doping a glass with praseodymiumand neodymium creates a color change when the type of light the glass issubjected to, exposed to or otherwise illuminated by, is changed.However, the colors observed when using pure Nd and Pr ions incombination is limited based on changes to the concentration of Nd andPr. For example, if the glass is used in anti-counterfeiting measures,the color shift of the glass could be replicated, for example, bycounterfeiters.

According to embodiments, to customize the color shift in Pr- andNd-containing silicate glasses, various chromophores can be added to theglass composition. The chromophores can be selected from ions of V, Cr,Mn, Fe, Ho, Co, Ni, Nb, Cu, Se, Bi, Er, Yb, and combinations thereof. Inembodiments, the ions of the above chromophores can be present asoxides. Each of these chromophores can be used to impart a unique colorshift when the light exposure is changed from incandescent tofluorescent. For example, when Co₃O₄ is added at about 0.0015 mole % tothe Pr- and Nd-containing silicate glass, the color shift of the glassis from violet to emerald when the incident light (illuminant) ischanged from incandescent to fluorescent light. When Co₃O₄ is added atabout 0.003 mole % to the Pr- and Nd-containing silicate glass, thecolor shift of the glass is from blue to teal when the incident light ischanged from incandescent to fluorescent light.

While one or more chromophores can be added to the Pr- and Nd-containingglasses of the disclosure, certain embodiments require someconsideration be given to ensuring that the metamerism associated withthe Nd₂O₃/Pr₂O₃ ratio and overall content is not overwhelmed by thechromophore dopant(s). For example, Co₃O₄ has a very stable blue color,and including too much Co₃O₄ in the glass composition will result in aglass that is blue under any light source. More particularly, Co₃O₄ at0.01 mole % or greater can overwhelm the pink-green-yellow hues of thePr- and Nd-containing glasses of the disclosure, resulting in only ablue color independent of the illumination source. Accordingly,embodiments employing Co₃O₄ (or CoO) as a chromophore in the glassshould limit Co₃O₄ (and CoO) to less than 0.01 mole %. Other embodimentsshould limit Co₃O₄ (and CoO) to less than 0.01*(Nd₂O₃+Pr₂O₃) in mole %.While Nb₂O₅ is typically not considered as a chromophore, it usuallyimparts a greenish color in high concentrations due to reduced Nbspecies and contaminants. Additionally, Nb₂O₅ is expensive and increasesthe density of the glass. Thus, it is desirable to control the Nb₂O₅content below 1 mole %, more preferably below 0.5 mole %, and mostpreferably less than 0.25 mole % to prevent the muddy green colorimparted by Nb₂O₅ from overwhelming or masking the colors observed fromthe otherwise multichroic nature of the glasses of the disclosure.Additional glass embodiments of the disclosure include Mn₂O₃ at lessthan 0.04 mole %. Still further, other embodiments of the disclosureinclude one or more chromophores selected from the group V₂O₅, Cr₂O₃,MnO, Mn₂O₃, Fe₂O₃, CoO, Co₃O₄, CuO, NiO, Nb₂O₅, CeO₂, Ho₂O₃ and Er₂O₃such that the sum of the chromophores included in the glass is less than0.1 mole % or, more preferably, less than 0.05 mole %. Inclusion oflarger concentrations of any of these chromophores, alone or incombination with each other, may affect the metamerism of the Pr- andNd-containing glasses of the disclosure.

In embodiments, the glass composition can comprise chromophores inconcentrations from greater than or equal to 0.001 mole % to less thanor equal to about 1.5 mole %, such as from greater than or equal toabout 0.01 mole % to less than or equal to about 1.0 mole %. In otherembodiments, the glass composition can comprise chromophores inconcentrations from greater than or equal to about 0.1 mole % to lessthan or equal to about 0.8 mole %, such as from greater than or equal toabout 0.15 mole % to less than or equal to about 0.6 mole %. In yetother embodiments, the glass composition can comprise chromophores inconcentrations from greater than or equal to about 0.2 mole % to lessthan or equal to about 0.5 mole %. In embodiments, the concentration ofthe secondary chromophores can be less than or equal to the Pr₂O₃ andNd₂O₃ concentrations to avoid overwhelming the metamerism of the Pr- andNd-containing glass. In other embodiments, the concentration of thesecondary chromophores can be less than or equal to one tenth of thePr₂O₃ and Nd₂O₃ concentrations to avoid overwhelming the metamerism ofthe Pr- and Nd-containing glass. In preferred embodiments, theconcentration of the secondary chromophores can be less than or equal toone hundredth of the Pr₂O₃ and Nd₂O₃ concentrations to avoidoverwhelming the metamerism of the Pr- and Nd-containing glass.

In addition to transition metal ion chromophores, embodiments of theglass compositions can comprise rare earth ions as colorants, which canbe present as rare earth oxides in embodiments. In embodiments, ions ofCe and Er can be added to the glass composition as rare earth ioncolorants. In embodiments, the glass composition comprises rare earthions in concentrations from greater than or equal to about 0.01 mole %to less than or equal to about 5.0 mole %, such as from greater than orequal to about 0.05 mole % to less than or equal to about 2.0 mole %. Inother embodiments, the glass composition includes Ce₂O₃ at aconcentration of less than 1 mole %. In another embodiment, the glasscomposition includes Er₂O₃ at a concentration of less than 1 mole %.Rare earth ions are weaker colorants than the transition metal ions and,thus, in embodiments, higher concentrations or rare earth ions can beneeded.

In embodiments, the glass composition can comprise SiO₂ in aconcentration from greater than or equal to about 40 mole % to less thanor equal to about 80 mole %, such as from greater than or equal to about50 mole % to less than or equal to about 75 mole %. In otherembodiments, the glass composition can comprise SiO₂ in a concentrationfrom greater than or equal to about 55 mole % to less than or equal toabout 70 mole %, such as from greater than or equal to about 62 mole %to less than or equal to about 69 mole %.

As discussed above, embodiments of the glass composition are directed toaluminosilicate glasses. Thus, the glass composition can comprise Al₂O₃in a concentration from greater than or equal to about 5.0 mole % toless than or equal to about 25 mole %, such as from greater than orequal to about 7.0 mole % to less than or equal to about 17 mole %. Inother embodiments, the glass composition can comprise Al₂O₃ in aconcentration from greater than or equal to about 8.0 mole % to lessthan or equal to about 14 mole %, such as from greater than or equal toabout 9.0 mole % to less than or equal to about 10 mole %. However, itshould be understood that the glass system is not particularly limitedand, thus, in some embodiments, glasses that contain from greater thanor equal to about 25% to less than or equal to about 50% Al₂O₃ can beused. In other embodiments, the glass system can include no Al₂O₃.

In embodiments, the glass composition can comprise Na₂O in aconcentration from greater than or equal to about 5 mole % to less thanor equal to about 25 mole %, such as from greater than or equal to about10 mole % to less than or equal to about 20 mole %. In otherembodiments, the glass composition can comprise Na₂O in a concentrationfrom greater than or equal to about 11 mole % to less than or equal toabout 17 mole %, such as from greater than or equal to about 12 mole %to less than or equal to about 15 mole %. In yet other embodiments, theglass composition can comprise Na₂O in a concentration of about 14 mole%.

In addition to Na₂O other alkali metal oxides can be included in theglass composition. In embodiments, the glass composition can includeLi₂O and/or K₂O. In some embodiments, the concentration of theadditional alkali metal oxides can be the same as the concentration ofNa₂O in the glass composition. In other embodiments, the concentrationof the additional alkali metal oxides can be different from theconcentration of Na₂O in the glass composition. However, in embodiments,the total concentration of alkali metal oxides in the glass compositioncan be less than or equal to about 18 mole %, such as less than or equalto about 16 mole %. In embodiment, the total concentration of alkalimetal oxides in the glass composition can be less than or equal to about14 mole %, such as less than or equal to about 12 mole %.

In embodiments, the glass composition can comprise Li₂O and/or K₂O in aconcentration from greater than or equal to about 2.0 mole % to lessthan or equal to about 10 mole %, such as from greater than or equal toabout 4.0 mole % to less than or equal to about 8.0 mole %. In otherembodiments, the glass composition can comprise Li₂O and/or K₂O in aconcentration from greater than or equal to about 6.0 mole % to lessthan or equal to about 7.0 mole %.

The glass composition can, in some embodiments, contain other elements,such as alkaline earth metal oxides. In embodiments, the alkaline earthmetal oxides can be selected from MgO, CaO, SrO, BaO, ZnO (which actssimilarly to alkaline earth metal oxides), and combinations thereof. Inembodiments, concentrations of alkaline earth metal oxides can be fromgreater than or equal to 0.0 mole % to less than or equal to about 25mole %, such as from greater than or equal to about 2.0 mole % to lessthan or equal to about 20 mole %. In other embodiments, the glasscomposition comprises alkaline earth metal oxides in concentrations fromgreater than or equal to about 10 mole % to less than or equal to about17 mole %, such as from greater than or equal to about 12 mole % to lessthan or equal to about 15 mole %.

In embodiments, the glass composition comprises each alkaline earthmetal oxide in concentrations from greater than or equal to 0.0 mole %to less than or equal to about 9.0 mole %, such as from greater than orequal to about 2.0 mole % to less than or equal to about 8.0 mole %. Inother embodiments, the glass composition comprises alkaline earth metaloxides in concentrations from greater than or equal to about 3.0 mole %to less than or equal to about 7.0 mole %, such as from greater than orequal to about 4.0 mole % to less than or equal to about 6.0 mole %. Inyet other embodiments, the glass composition comprises alkaline earthmetal oxides in concentrations of about 5.0 mole %.

Fluorescent Glasses

Embodiments of the glass composition can include fluorescent ions. Insome embodiments, the fluorescent ions are used in place of thechromophores. However, in other embodiments, the fluorescent ions arepresent in addition to the chromophores. In embodiments, the fluorescentions can be selected from ions of Cu, Sn, Mn, Sb, Ag, Ce, Sm, Eu, Tb,Dy, Tm, and combinations thereof. In embodiments, the fluorescent ionscan be present as oxides.

Using fluorescent ions allows the glass composition to emit differentcolors of visible light when the glass is excited with certainwavelengths of light. Fluorescent ions can be added to the Pr- andNd-containing glasses of the disclosure without imparting any visiblecolor, and yet enable the glass to fluoresce under UV light-inducedexcitation. In embodiments, the color of the fluorescent ion can emitone color when excited with light of a first wavelength (365 nm, forexample) and it can emit a second color when excited with light at asecond wavelength (405 nm, for example). For example, Eu³⁺ doped glassand Tb³⁺ doped glass, whether Pr- and Nd-containing or not, emits redlight and green light, respectively, when exposed to 365 nm light.

In embodiments, the glass composition can comprise fluorescent ions inconcentrations from greater than or equal to 0.01 mole % to less than orequal to about 5.0 mole %, such as from greater than or equal to about0.05 mole % to less than or equal to about 2.0 mole %. In otherembodiments, the glass composition can comprise fluorescent ions inconcentrations from greater than or equal to about 0.1 mole % to lessthan or equal to about 1.0 mole %, such as from greater than or equal toabout 0.15 mole % to less than or equal to about 0.6 mole %. In yetother embodiments, the glass composition can comprise fluorescent ionsin concentrations from greater than or equal to about 0.2 mole % to lessthan or equal to about 0.5 mole %.

Multi-Fluorescent Glasses

Embodiments of the glass composition can include two or more differentfluorescent ions. In embodiments, the fluorescent ions can be selectedfrom Cu, Sn, Mn, Sb, Ce, Sm, Eu, Tb, Tm, Sm, Dy, and combinationsthereof. In embodiments, the fluorescent ions can be present as oxides.Using multiple fluorescent ions allows the glass composition to emitdifferent colors of visible light when the glass is excited with certainwavelengths of light. In embodiments, the glass composition canfluoresce a first color at a first wavelength that is from greater thanor equal to about 300 nm to less than or equal to about 400 nm, such asfrom greater than or equal to about 310 nm to less than or equal toabout 390 nm. The glass composition can fluoresce a second color at asecond wavelength that is from greater than or equal to about 400 nm toless than or equal to about 475 nm, such as from greater than or equalto about 410 nm to less than or equal to about 465 nm. The glasscomposition can fluoresce a third color at a third wavelength that isfrom greater than or equal to about 475 nm to less than or equal toabout 500 nm, such as from greater than or equal to about 480 nm to lessthan or equal to about 495 nm.

For example, in embodiments, the color of the fluorescent ion can emitone color when excited with light of a first wavelength (365 nm, forexample), it can emit a second color when excited with light at a secondwavelength (405 nm, for example), and it can emit a third color whenexcited with light at a third wavelength (488 nm, for example). Forexample, embodiments can include glasses comprising oxides of Eu andoxides of Tb as its fluorescent ions. Eu³⁺ doped glasses generally emitred when excited with the proper wavelength of light, and Tb³⁺ dopedglasses generally emit green when excited with the proper wavelength oflight. However, when Eu oxides and Tb oxides are combined in a glasscomposition, the glass composition can emit light that is red, green,orange, yellow, or a combination of those colors upon being excited bylight having a wavelength of 365 nm, with the exact color depending onthe proportional mixture of Eu³⁺ and Tb³⁺ ions in the glass. However,when the glass is excited with light at a 405 nm wavelength, only theEu³⁺ is excited and red light is emitted, and when the glass is excitedwith 488 nm light, only the Tb³⁺ is excited and green light is emittedwhen the Eu³⁺ concentration is sufficiently low to prevent energytransfer from Tb³⁺ to Eu³⁺. The Eu₂O₃ content in the glass should beless than about 0.1 mole % to prevent energy transfer, and preferablyless than 0.05 mole %. Accordingly, embodiments of the glass can beconfigured to emit three distinct colors depending on the wavelength ofthe light used to excite the glass composition. If the glass is meltedin slightly reducing conditions, some or all of the Eu³⁺ can be reducedto Eu²⁺ which emits blue light when excited at wavelengths below 400 nm.Such a glass co-doped with Tb³⁺ will emit white (Eu²⁺, Eu³⁺, and Tb³⁺emission) light when excited at wavelengths of about 365 nm, purple(Eu²⁺ and Eu³⁺ emission) when excited at wavelengths of about 394 nm,blue (Eu²⁺ emission, only) when excited at wavelengths of about 310 orabout 330 nm, aqua (Eu²⁺ and Tb³⁺ emission) when excited at wavelengthsof about 342 nm, green (Tb³⁺ emission only) when excited at wavelengthsof about 484 nm, and red (Eu³⁺ emission only) when excited atwavelengths of about 464 nm.

Some fluorescent ions can cross relax or quench each other, so theselection and concentration of each ion has to be engineered to ensureboth ions are emitting. For example, when the concentration of Eu₂O₃exceeds about 2 mole %, in a Tb³⁺ emitting glass, most of the excitedTb³⁺ ions can transfer their energy to neighboring Eu³⁺ ions and onlythe red emission of the Eu³⁺ ion can be left even if the excitationwavelength only excites the Tb³⁺ ion. This energy transfer mechanism canalso be used to sensitize a fluorescent ion to increase the effectiveabsorption of pump energy. As another example, the inclusion of a CeO₂dopant should be balanced against Eu₂O₃ and Tb₂O₃, if present. Since theCe⁴⁺ ion is an allowed f-d transition while the other rare earthelements are exemplified by forbidden f-f transitions, the Ce⁴⁺ f-dtransition is orders of magnitude stronger than those of other rareearth elements. Thus, the CeO₂ content should not exceed the content ofEu₂O₃ and that of Tb₂O₃, if either are present, otherwise the blueemission of the Ce₂O₃ will overwhelm the weaker red Eu³⁺ and green ofthe Tb³⁺ ions.

In embodiments, the glass composition can comprise two or morefluorescent ions in concentrations from greater than or equal to 0.01mole % to less than or equal to about 5 mole %, such as from greaterthan or equal to about 0.05 mole % to less than or equal to about 2.0mole %. In other embodiments, the glass composition can comprise two ormore fluorescent ions in concentrations from greater than or equal toabout 0.1 mole % to less than or equal to about 1 mole %, such as fromgreater than or equal to about 0.15 mole % to less than or equal toabout 0.6 mole %. In yet other embodiments, the glass composition cancomprise two or more fluorescent ions in concentrations from greaterthan or equal to about 0.2 mole % to less than or equal to about 0.5mole %.

In addition to fluorescent ions, embodiments of the glass compositionscan comprise rare earth ions as colorants. In embodiments, the rareearth ions can be present as rare earth oxides. In embodiments, ions ofEr and Ce can be added to the glass composition as rare earth ioncolorants. In embodiments, the ions of Er and Ce can be present in theglass as oxides. In embodiments, the concentration of rare earth ion inthe glass composition can be less than the concentration of fluorescentions in the glass composition. In some embodiments, the concentration ofCe₂O₃ in the glass composition is less than the concentration offluorescent ions in the glass composition.

The multi-fluorescent glasses can also be doped with transition metalions to impart color in addition to the multi-fluorescent effect. If theglass is strongly absorbing near the fluorescence wavelength, then thefluorescence will be absorbed or quenched. To avoid fluorescencequenching, the concentration of these dopants should be kept below 0.5mole % and for strong chromophores like Co²⁺ and Ni²⁺ ions, below 0.1mole %. In cases where the absorption of the chromophores overlaps thefluorescence (such as the case where the red emission of Eu³⁺ would beannihilated by the red absorption of the Co²⁺), the chromophoreconcentration should be below 0.02 mole %.

In embodiments, the glass composition comprises rare earth ions inconcentrations from greater than or equal to about 0.1 mole % to lessthan or equal to about 10 mole %, such as from greater than or equal toabout 0.2 mole % to less than or equal to about 7.0 mole %. In otherembodiments, the glass composition comprises rare earth ions inconcentrations from greater than or equal to about 0.3 mole % to lessthan or equal to about 5.0 mole %, such as from greater than or equal toabout 0.4 mole % to less than or equal to about 3.0 mole %. In yet otherembodiments, the glass composition comprises rare earth ions inconcentrations from greater than or equal to about 0.5 mole % to lessthan or equal to about 2.0 mole %, such as from greater than or equal toabout 0.8 mole % to less than or equal to about 1.0 mole %.

Color-changing glasses according to embodiments may be used in manydifferent applications. For example, glasses that change color can beused as aesthetic embellishments on, for example, clothing, electronics(e.g., cell phone backs and cases), and packaging (e.g., perfumebottles). These color-changing glasses can also be employed in artworkthat changes color depending on the lighting conditions. Small energyefficient LEDs can be included in the device, packaging, art work,sculpture and other products and forms that incorporate these glasses toensure that the fluorescent and/or absorptive color(s) of these glassescan be changed by illuminating the glass composition with light ofdiffering wavelengths. Color-tunable white LEDs that consist ofindividually addressable red, green and blue LEDs can be augmented witha UV LED and a broad-band phosphor LED so that the color can be changedby these LEDs, or embedded in the base or edges of the glass forstunning and amazing color visual effects. Waveguides can also beembedded into the glass for even more complex visual effects where thelight sources themselves are out of view.

Further, color-changing glasses can be used as anti-counterfeitingsystems. For example, glasses according to embodiments can be formed tohave a first customized color in broad spectrum white light and a secondcustomized color in fluorescent light, or a glass can be formed tofluoresce customized colors by using different fluorescent ions. In thisway it can be easy to detect whether a good is counterfeit by simplyobserving the color of the glass in different sources of white light.

It should now be understood that glass compositions described herein arecolor-changing glasses that include praseodymium and neodymium,chromophore(s) and/or fluorescent ion(s). Preferably, these glassesinclude praseodymium and neodymium, and optionally containchromophore(s) and/or fluorescent ion(s). The various combinations ofone or more of praseodymium and neodymium; chromophore(s); andfluorescent ion(s) allow the color of the glass to be customizable andchangeable depending on the lighting exposure. The customizable andchangeable color allows the glass to be used as decorative glass and asan anti-counterfeiting scheme. For example, a glass can include Eu²⁺ andTb³⁺ ions so that the glass emits blue (Eu²⁺ emission, only) whenexcited at wavelengths of about 310 or about 330 nm, aqua (Eu²⁺ and Tb³⁺emission) when excited at wavelengths of about 342 nm, green (Tb³⁺emission only) when excited at wavelengths of about 484 nm. This glasscan then be exposed to these different wavelengths of light and if itdoes not fluoresce properly, it can be determined that the good iscounterfeit. Using this anti-counterfeiting system, counterfeit goodscan easily and quickly be detected. In contrast, many knownanti-counterfeiting schemes have been developed that use secretive,expensive “black box” sensors to indicate whether a good is genuine orcounterfeit. However, many of these anti-counterfeiting schemes requirespecialized equipment, which is generally not available to consumers, todetermine whether a good is genuine or counterfeit. There is also aproblem with counterfeit “black boxes” that falsely indicate a productis genuine. Further, the anti-counterfeit schemes often cannot beincorporated into the article in an aesthetically pleasing manner.

In addition to being added as aesthetic embellishments, glassesaccording to embodiments may be used as bottles and containers forgoods. For example, perfumes, colognes, liqueurs, medicines, andelectronics are frequently counterfeited and, thus, the containers forthese goods can be made from color-changing glasses, according toembodiments disclosed herein. To meet these various uses, glasses,according to embodiments, may be formed into articles such as bottlesand glass sheets by any suitable glass forming method. For example,color-changing glass bottles may be made in numerous shapes and sizes byglass forming methods including, for example, blow molding, punchmolding, punch and blow molding, and other suitable molding processes.Color-changing glasses, according to some embodiments, may be formedinto glass sheets that may be applied, for example, to electronics bymethods such as, for example, floating or fusion drawing as disclosed inU.S. Pat. Nos. 3,338,696 and 3,682,609, which are herein incorporated byreference in its entireties.

In some embodiments, glasses disclosed herein can be subjected tophysical or chemical strengthening. For example, the glasses can betempered by heat treatments or strengthened by ion exchange. In anion-exchange process, the glass may be exposed to an alkali ioncontaining solution, such as, for example, KNO₃ or NaNO₃. Upon exposureto the alkali ion containing solution, smaller alkali ions in the glass,such as, for example, Li and Na ions, are exchanged with larger ions,such as, for example, Na and K. This ion exchange reinforces the glassmatrix and can strengthen the glass. In certain implementations, thestrengthening results in the development of a compressive stress regionwith a maximum compressive stress (typically at one or more primarysurfaces of the glass) of at least 50 MPa that spans a depth within theglass (referred herein as a “depth of layer” or “DOL”). Typical DOLlevels are at least 15 microns in thickness. Suitable ion exchangemethods are disclosed in U.S. Pat. No. 5,674,790, which is hereinincorporated by reference in its entirety. In addition to strengtheningthe glasses, the strengthening process can make the glass compositionsfrangible so that if the glass is tampered with it will shatter. Inanti-counterfeiting systems, the frangibility of the glass is abeneficial anti-tampering element.

EXAMPLES

Embodiments will be further clarified by the following examples whichare intended to be non-restrictive and illustrative only.

Example 1

Praseodymium- and Neodymium-Containing Glasses

Glass compositions having the compositions disclosed in Tables 1 and 2below were prepared by mixing 1 kg batches of sand, aluminum oxide,sodium sulfate, potassium nitrate, magnesium oxide, calcium carbonate,barium carbonate, zinc oxide, borax, praseodymium oxide, and neodymiumoxide, along with cobalt oxide for certain examples. The batches werethen loaded in a platinum crucible, and melted for 5 hours at 1325° C.and then poured into a bucket of water to make a cullet. The cullet wasthen crushed and re-melted for 6 hours at 1475° C. to homogenize theglass. The melts were then poured onto a steel table, and annealed at550° C. for 2 hours before cooling to room temperature. The resultingglass patties were cut into glass samples, which were then polished forpurposes of color determinations and color coordinate measurements. Inparticular, the glass samples were polished to smooth their exteriorsurfaces, thus improving optical quality and reducing scattering oflight passing through the thickness of the samples during colorcoordinate measurements. As understood by those with ordinary skill inthe field of the disclosure, polishing times and conditions were variedbased on the size of the samples for purposes of making colordeterminations and color coordinate measurements.

Examples 1-7 (“Exs. 1-7”) in Table 1 are directed to glasses comprisingpraseodymium and neodymium that appear according to embodimentsdisclosed herein. In these examples, the praseodymium levels ranged from0.7 mole % to 0.9 mole % and the neodymium levels ranged from 1.1 mole %to 1.3 mole %. Further, the ratios of praseodymium to neodymium rangedfrom 1.222 (Exs. 1, 7) to 1.857 (Ex. 5). All of these examples aremultichroic glasses that exhibit metamerism. In particular, each of themappears pink upon exposure to incandescent or daylight, green uponexposure to fluorescent light and yellow upon exposure to LED light. Forexample, Ex. 1 is green under fluorescent light with nearly the samecolor as a glass doped with Pr³⁺ ions alone without Nd³⁺ ions. Yet thetrue color of the glass in Ex. 1 in daylight, incandescent or fullspectrum white light is pink. Further, under LED illumination, such asmodern low energy consumption fixtures or LED flashlights, the glassappears yellow.

Examples 8-11 (“Exs. 8-11”) in Table 1 are directed to glassescomprising praseodymium and neodymium and at least one chromophore(e.g., Co₃O₄) according to embodiments disclosed herein. Ex. 8-11 inTable 1 show that even though the Pr₂O₃ concentration is 0.7 to 0.8 mole%, the Nd₂O₃ concentration is 1.2 to 1.3 mole % and the Co₃O₄concentration ranges from 0.0029 to 0.0133 mole %, the metamerism comesthrough and the samples appear violet, blue, blue or purple inincandescent or full spectrum white light, and emerald, teal, greenishblue or green in fluorescent light, respectively. Hence, maintaining theCoO to concentration levels below 0.015 mole % (or, alternatively, C0304to concentration levels below 0.01 mole %) ensures that thesepraseodymium- and neodymium-containing glasses retain metamerism afterbeing doped with a chromophore.

Table 2 shows the corresponding color coordinates in L*, a*, b* space asa function of standard illumination conditions for Ex. 1, as measuredthrough the thickness of the sample (a 40×40 mm square test coupon witha thickness provided below) in reflectance mode on an X-Rite Color i7™Benchtop Spectrophotometer with a white backing substrate situatedbehind the sample. D65 is natural daylight, F-02 is fluorescent light,and A-10 corresponds to incandescent light. The reported colordifference (CD) data was obtained using Equation (1). There aresubstantial shifts in the color coordinates between the full spectrumwhite light and fluorescent illuminants. Notably, the F02 to A10 (i.e.,“CD (F02-A10)” as shown in Table 2) sequence shows the greatest colordifference (CD) for this glass at 17.53.

TABLE 1 Praseodymium- and Neodymium-Containing Glasses Absorptive ColorIllumination Composition (mole %) Incan- Fluores- Glass SiO₂ Al₂O₃ Na₂OK₂O MgO CaO BaO ZnO B₂O₃ Nd₂O₃ Pr₂O₃ Nd:Pr CoO descent cent Ex. 1 71.11.09 16.13 0.39 0.11 5.87 0.95 0.78 1.56 1.081 0.884 1.222 0 Pink GreenEx. 2 71.1 1.09 16.13 0.39 0.11 5.87 0.95 0.78 1.56 1.179 0.786 1.5 0Pink Green Ex. 3 71.1 1.09 16.13 0.39 0.11 5.87 0.95 0.78 1.56 1.0810.884 1.222 0 Pink Green Ex. 4 71.1 1.09 16.13 0.39 0.11 5.87 0.95 0.781.56 1.179 0.750 1.573 0 Pink Green Ex. 5 71.1 1.09 16.13 0.39 0.11 5.870.95 0.78 1.56 1.277 0.688 1.857 0 Pink Green Ex. 6 71.1 1.09 16.13 0.390.11 5.87 0.95 0.78 1.56 1.179 0.786 1.5 0 Pink Green Ex. 7 71.1 1.0916.13 0.39 0.11 5.87 0.95 0.78 1.56 1.081 0.884 1.222 0 Pink Green Ex. 871.1 1.09 16.13 0.39 0.11 5.87 0.95 0.78 1.56 1.179 0.786 1.5 0.0044Violet Emerald Ex. 9 71.1 1.09 16.13 0.39 0.11 5.87 0.95 0.78 1.56 1.1790.786 1.5 0.0088 Blue Teal Ex. 10 71.1 1.09 16.13 0.39 0.11 5.87 0.950.78 1.56 1.179 0.786 1.5 0.0133 Blue Greenish Ex. 11 71.1 1.09 16.130.39 0.11 5.87 0.95 0.78 1.56 1.277 0.688 1.856 0.0029 Purple Green

TABLE 2 Reflective Color Coordinates A-10 F02-10 CD CD CD GlassThickness D65-10 (CWF) (D65- (F02- (D65- Composition (mm) L* a* b* L* a*b* L* a* b* F02) A10) A10) Ex. 1 2 70.75 −3.97 9.09 68.25 −12.16 7.0570.98 4.9 10.03 8.80 17.53 8.92 Ex. 2 5.71 56.42 7.4 17.89 55.44 −8.7119.75 58.5 15.78 23.91 16.25 25.03 10.53 Ex. 3 5.73 57.04 6.29 20.1556.04 −9.51 22.08 59.1 14.98 26.41 15.95 25.06 10.91 Ex. 4 Ex. 5 5.7356.35 8.95 13.11 55.33 −7.77 14.83 58.36 16.37 19.18 16.84 24.72 9.79Ex. 6 5.71 56.42 7.4 17.89 55.44 −8.71 19.75 58.5 15.78 23.91 16.2525.03 10.53 Ex. 7 5.73 57.04 6.29 20.15 56.04 −9.51 22.08 59.1 14.9826.41 15.95 25.06 10.91 Ex. 8 5.71 44.65 1.75 −0.46 43.62 −11.63 1.0944.97 4.13 3.67 13.51 16.03 4.78 Ex. 9 5.72 35.66 1.88 −13.43 34.53−10.52 −12.18 34.88 −2.14 −10.3 12.51 8.60 5.15 Ex. 10 5.7 27.8 5.36−25.16 26.42 −6.72 −24.54 25.97 −6.7 −23.15 12.17 1.46 12.36 Ex. 11 5.7348.03 4.48 3.11 47.05 −10.02 4.69 48.92 8.67 7.63 14.62 19.01 6.23

Example 2

Multi-Fluorescent Glasses

Glass compositions having the compositions disclosed in Table 3 belowwere prepared by mixing 1 kg batches of sand, aluminum oxide, sodiumcarbonate, sodium sulfate, potassium nitrate, magnesium oxide, calciumcarbonate, barium carbonate, zinc oxide, and borax, along with europiumoxide, terbium oxide, cerium oxide and/or lanthanum oxide, loading themin a platinum crucible, and melting for 6 hours at 1475° C. The meltswere then poured onto a steel table, and then annealed at 530° C. for 2hours before cooling to room temperature. The resulting glass pattieswere cut into glass samples, which were then polished for purposes ofcolor determinations. In particular, the glass samples were polished tosmooth their exterior surfaces, thus improving optical quality. Asunderstood by those with ordinary skill in the field of the disclosure,polishing times and conditions were varied based on the size of thesamples for purposes of making color determinations.

In particular, Examples 12-18 in Table 3 are directed to glassescomprising multiple fluorescent ions according to embodiments disclosedherein, without the presence of praseodymium and neodymium. As such,they are clear unless exposed to certain ultraviolet wavelengths (e.g.,365 nm and 405 nm ultraviolet light). For example, the Ex. 15 glasscontains both Eu³⁺ and Tb³⁺ ions and glows yellow when excited at 365 nmdue to the emission of both of its Eu³⁺ and Tb³⁺ ions. However, the sameglass glows red when excited at 405 nm, since the 405 nm light onlyexcites the red emitting Eu³⁺ ions. It also glows green when excited at488 nm which preferentially excites the green emitting Tb³⁺ ions.

It should also be understood that other embodiments of praseodymium- andneodymium-containing glasses in the disclosure with the same or similarconcentrations of fluorescent dopants, as shown in the Examples in Table3, can demonstrate metamerism. Additionally, such praseodymium- andneodymium-containing glasses can exhibit the same fluorescent colors asthe Examples in Table 3 upon excitation with ultraviolet (UV) light ofparticular wavelengths (e.g., 365 nm and 405 nm light). Table 4 showsthe corresponding color coordinates for one of the glass compositionsprovided in Table 3.

TABLE 3 Multi-Fluorescent Glasses Fluorescent Color ExcitationWavelength Composition (mole %) 365 405 Glass SiO₂ Al₂O₃ Na₂O K₂O MgOCaO BaO ZnO B₂O₃ Nd₂O₃ Pr₂O₃ Eu₂O₃ Tb₂O₃ CeO₂ La₂O₃ nm nm Ex. 71.1 1.0916.13 0.39 0.11 5.87 0.95 0.78 1.56 0 0 0    0     0.39 1.765 Blue Sky12 blue Ex. 71.1 1.09 16.13 0.39 0.11 5.87 0.95 0.78 1.56 0 0 0    1.8650.2  0    Aqua None 13 Ex. 71.1 1.09 16.13 0.39 0.11 5.87 0.95 0.78 1.560 0 0    1.965 0   0    Green None 14 Ex. 71.1 1.09 16.13 0.39 0.11 5.870.95 0.78 1.56 0 0 0.491 1.474 0   0    Yellow Red 15 Ex. 71.1 1.0916.13 0.39 0.11 5.87 0.95 0.78 1.56 0 0 0.786 1.179 0   0    Orange Red16 Ex. 71.1 1.09 16.13 0.39 0.11 5.87 0.95 0.78 1.56 0 0 1.965 0   0  0    Red Red 17 Ex. 71.1 1.09 16.13 0.39 0.11 5.87 0.95 0.78 1.56 0 01.566 0   0.78 0    Red Red 18

TABLE 4 Reflected Color Coordinates A-10 CD CD CD Glass Thickness D65-10F02-10(CWF) (D65- (F02- (D65- Composition (mm) L* a* b* L* a* b* L* a*b* F02) A10) A10) Ex. 12 Ex. 13 Ex. 14 Ex. 15 Ex. 16 Ex. 17 Ex. 18 289.19 −0.15 5.88 89.47 −0.03 6.43 89.57 1.46 5.95 0.63 1.57 1.66

As discussed above, in embodiments, colorants, chromophores, andfluorescent ions can be present in the glass as oxides of theirrespective components. Accordingly, it should be understood that whenreferring to oxides of colorants, chromophores, and fluorescentshereinabove, the colorants, chromophores, and fluorescents can bepresent as compounds other than oxides.

It will be apparent to those skilled in the art that variousmodifications and variations can be made to the embodiments describedherein without departing from the spirit and scope of the claimedsubject matter. For example, the color-changing and multichroic glasscompositions of the disclosure can be combined in various forms withother color-changing glasses, e.g., the glasses contained inInternational Publication No. WO2015/077136 (“WO '136 reference”),published on May 28, 2015, claiming the benefit of U.S. ProvisionalApplication No. 61/905,958, filed Nov. 19, 2013, both of which arehereby incorporated by reference in their entirety. In one exemplaryform, a composite structure of alternating glass layers comprising thePr- and Nd-containing pink-to-green glass of this disclosure and aholmium-containing green-to-pink glass of the WO '136 reference can beformed for use in an anti-counterfeiting feature or scheme. As such, itis intended that the specification cover the modifications andvariations of the various embodiments described herein, provided thatsuch modifications and variations come within the scope of the appendedclaims and their equivalents.

What is claimed is:
 1. A glass, comprising: Pr₂O₃ ranging from 0.7 to3.0 mole %; and Nd₂O₃, ranging from 1.0 to 4 mole %, wherein and theratio of Nd₂O₃ to Pr₂O₃ is greater than 1.1 and less than 1.5, andfurther wherein CoO, if present, is less than 0.01 mole % and Fe₂O₃, ifpresent, is less than 0.004 mole %.
 2. The glass according to claim 1,wherein Nb₂O₅, if present, is less than 0.5 mole %, Ce₂O₃, if present,is less than 1 mole %, and Er₂O₃, if present, is less than 1 mole %. 3.The glass according to claim 1, further comprising: one or morefluorescent ions selected from the group consisting of oxides of Yb, Cu,Sn, Mn, Ag, Sb, Ce, Sm, Eu, Tb, Dy, Tm, and combinations thereof,wherein a total concentration of fluorescent ions is from greater thanor equal to about 0.01 mole % to less than or equal to about 5.0 mole %.4. A glass, comprising: Pr₂O₃; and Nd₂O₃, wherein (Pr₂O₃+Nd₂O₃) isgreater than 0.2 mole % and the ratio of Nd₂O₃ to Pr₂O₃ is greater than1 and less than 1.9, and further wherein CoO, if present, is less than0.01 mole % and Fe₂O₃, if present, is less than 0.004 mole %, and one ormore chromophores selected from the group consisting of V₂O₅, Cr₂O₃,MnO, Mn₂O₃, Fe₂O₃, CoO, CO₃O₄, CuO, NiO, Nb₂O₅, CeO₂, Ho₂O₃ and Er₂O₃,wherein the sum of V₂O₅, Cr₂O₃, MnO, Mn₂O₃, Fe₂O₃, CoO, CO₃O₄, CuO, NiO,Nb₂O₅, CeO₂, Ho₂O₃ and Er₂O₃ chromophores is less than 0.1 mole %. 5.The glass according to claim 1, wherein the glass is characterized by afirst color upon exposure to an incandescent light source and a secondcolor upon exposure to a fluorescent light source, the first and secondcolors distinct from one another.
 6. The glass according to claim 1,wherein the glass is further characterized by a color difference (CD) ofat least 3.0 from being subjected to a D65-10 illumination condition andan F02-10 illumination condition.
 7. A glass, comprising: Pr₂O₃ rangingfrom 0.7 to 3.0 mole %, and Nd₂O₃ ranging from 1.0 to 4 mole %, whereinthe ratio of Nd₂O₃ to Pr₂O₃ is greater 1.1 and less than 1.5, andfurther wherein the sum of V₂O₅, Cr₂O₃, MnO, Mn₂O₃, Fe₂O₃, CoO, CO₃O₄,CuO, NiO, Nb₂O₅, CeO₂, Ho₂O₃ and Er₂O₃ chromophores, if any of thechromophores are present, is less than 0.1 mole %.
 8. The glassaccording to claim 7, wherein Mn₂O₃, if present, is less than 0.04 mole%.
 9. The glass according to claim 7, further comprising: one or morechromophores selected from the group consisting of V₂O₅, Cr₂O₃, MnO,Mn₂O₃, Fe₂O₃, CoO, Co₃O₄, CuO, NiO, Nb₂O₅, CeO₂, Ho₂O₃ and Er₂O₃.
 10. Aglass, comprising: Pr₂O₃; and Nd₂O₃, wherein (Pr₂O₃+Nd₂O₃) is greaterthan 0.2 mole % and the ratio of Nd₂O₃ to Pr₂O₃ is greater than 0.5 andless than 3, and further wherein the sum of V₂O₅, Cr₂O₃, MnO, Mn₂O₃,Fe₂O₃, CoO, CO₃O₄, CuO, NiO, Nb₂O₅, CeO₂, Ho₂O₃ and Er₂O₃ chromophores,if any of the chromophores are present, is less than 0.1 mole %, and oneor more fluorescent ions selected from the group consisting of oxides ofYb, Cu, Sn, Mn, Ag, Sb, Ce, Sm, Eu, Tb, Dy, Tm, and combinationsthereof, wherein a total concentration of fluorescent ions is fromgreater than or equal to about 0.01 mole % to less than or equal toabout 5.0 mole %.
 11. The glass according to claim 7, wherein the glassis characterized by a first color upon exposure to an incandescent lightsource and a second color upon exposure to a fluorescent light source,the first and second colors distinct from one another.
 12. The glassaccording to claim 7, wherein the glass is further characterized by acolor difference (CD) of at least 3.0 from being subjected to a D65-10illumination condition and an F02-10 illumination condition.
 13. Aglass, comprising: SiO₂ at greater than 70 mole %; Pr₂O₃ ranging from0.7 to 3.0 mole %; and Nd₂O₃ ranging from 1.0 to 4 mole %, wherein theratio of Nd₂O₃ to Pr₂O₃ is greater than 1.1 and less than 1.5, andfurther wherein the sum of Fe₂O₃, CeO₂, and TiO₂, if any are present, isless than 1 mole %.
 14. The glass according to claim 13, wherein the sumof Mn₂O₃, Fe₂O₃, NiO and CeO₂, if any are present, is less than 2 mole%.
 15. A glass article, comprising: a substrate comprising a glassaccording to claim 12, wherein the substrate further comprises acompressive stress region having a maximum compressive stress of atleast 50 MPa and a depth of layer (DOL) of at least 15 microns inthickness.
 16. A glass article, comprising: a substrate comprising aglass according to claim 1, wherein the substrate further comprises acompressive stress region having a maximum compressive stress of atleast 50 MPa and a depth of layer (DOL) of at least 15 microns inthickness.
 17. A glass article, comprising: a substrate comprising aglass according to claim 13, wherein the substrate further comprises acompressive stress region having a maximum compressive stress of atleast 50 MPa and a depth of layer (DOL) of at least 15 microns inthickness.